1. Technical Field of the Invention
The present invention relates generally to improvements on a two-dimensional code made up of a matrix of data cells carrying optically readable binary-coded information and an optical code reading method of reading such a two-dimensional code.
2. Background Art
U.S. Pat. No. 5,726,435 filed Mar. 10, 1998, assigned to the same assignee as that of this application, teaches a two-dimensional code used in inputting information into a computer.
Typical two-dimensional codes have a two-dimensional spread, as shown in FIG. 1(b), which can carry a large amount of information in a narrow area as compared with a bar code, as shown in FIG. 1(a), but the structure thereof is complex.
FIG. 2 shows one example of two-dimensional codes. The two-dimensional code 500 includes three location symbols 510a, 510b, and 510c and arrays of timing cells 520a and 520b. The location symbols 510a to 510c are used in locating the two-dimensional code 500 and each consist geometrically of a plurality of squares different in size. The arrays of timing cells 520a and 520b are each disposed between adjacent two of the location symbols 510a to 510c and consist of a plurality of white and black cells arranged in a reference pattern that are used as indices of data cells arranged in a data field 530.
The two-dimensional code 500 is made up of a square matrix of n.times.n cells. Each of the location symbols 510a to 510c consists of a frame-like black square 512 formed with four sides each consisting of 7 cells, a frame-like white square 514 formed with four sides each consisting of 5 cells, and a black square 516 consisting of 3.times.3 cells formed on the central portion of the white square 514.
When each of the location symbols 510a to 510c is scanned through an optical reader along any line passing through the center thereof, an optical signal pattern which has a brightness component ratio of black:white:black:white:black=1:1:3:1:1 is detected. Thus, when an optical signal pattern having that brightness component ratio is detected during scanning of the two-dimensional code 500, it may be determined as a candidate pattern for any one of the location symbols 510a to 510c. Specifically, when three optical signal patterns each having a brightness component ratio of 1:1:3:1:1 are detected, it may be determined that the two-dimensional code 500 lies on a square area defined by the three optical signal patterns.
The data field 530 consists of data cells (not shown for the brevity of illustration) each formed with a black or white square indicating logical 0 or 1 of a binary-coded data. Two-dimensional coordinates of each data cell are determined in a known algorithm by using the centers of the location symbols 510a to 510c and the timing cells 520a and 520b as indices of the coordinates.
Usually, the size of each cell of such a two-dimensional code is required to be adjusted to individual uses. For example, optically reading a two-dimensional code printed on a label attached to an article being conveyed at high speeds requires increasing the size of each cell. However, for a two-dimensional code printed on an article being conveyed at low speeds or resting, the size of each cell may be small.
For instance, sorting a large number of articles automatically, may be achieved by transporting the articles at high speeds and optically reading two-dimensional codes printed thereon. In contrast, an operator may sort the articles manually by reading the two-dimensional codes using a hand-held optical reader. In this case, it is advisable that the two-dimensional code be made up of the smallest possible cells to reduce the overall size thereof.
In order to meet the above two requirements, it is necessary to make two-dimensional codes of two sizes. This, however, consumes much time of the operator in preparing and attaching two-dimensional code-printed labels to the articles. The two-dimensional code may alternatively be made which consists of two sections: one carrying data to be read out during transportation of the articles at high speeds, and the second carrying data to be read out during transportation of the articles at low speeds. However, the size of each cell needs to be fitted for the high speed transportation, thus resulting in an increased overall size of the two-dimensional codes. This also requires a large-sized optical reader.